Any disadvantages to horizontal repipe now and vertical later?

In reference to a couple of threads today, I'm just wondering if there is any disadvantage to getting the horizontals repiped now and putting off the verticals until some of our summer vacation, guests, etc. are over and done with?

I know the general consensus is to NOT do a partial repipe (ie, all or nothing), but if I want to at least take care of the attic pipes soon, but put off the verticals until we're ready to focus on some remodeling, etc., are there any downsides to doing this technically, financially or for any other reason?

Financially,
You have the plumbers in there working, and then you bring them back. Rather then remove parts and then reattach, it's easier to cut out and replace. It saves time to remove and replace. Fitting new pipe into old pipe takes time.

Electrolysis, Anytime you move between copper and galvanized, you shorten the life of the existing galvanized pipe. Copper and steel are not real compatible.

As you turn off the water and then bring it back on, the end parts of the runs will break out crud from the inside of the pipe. That winds up in the cartridges and the aerators. You will wind up doing some flushing.

Most of the slow down in the pipe will be where the most electrolysis has occurred. That is any place where brass meets steel. That means the shutoffs at the wall have the most reduction. A attic repipe hasn't done anything for those connections.
Tub and shower valves, these are made of brass, same problem there. The steel will corrode and close off where it meets the brass.

Replacing the horizontals may help a little, but also speeds the demise of the pipe that has been left behind.

I see. But if I'm going from gal to either PEX or CPVC, then electrolysis shouldn't be as big an issue, right? There are a few copper pipes up in the attic here and there, apparently where the previous owners had leaks from gal and replaced with copper.

Also, from a pure "leak prevention" point of view though, wouldn't it be prudent to at least get the horizontals done now rather than wait until a time when it's good to do the verticals as well?

Our only hesitation with doing the verticals now is with wall destruction. The plumber I got a quote from last night said there will be less destruction with PEX as opposed to CPVC. We also have access panels to 3 out of the 4 bathtubs, so he said they wouldn't need to break any walls to replumb down to those tubs b/c of the access panels. For vanities, he said they can do 12 x 12 inch holes under the sinks to access the lines. Kitchen will require the dishwasher to be pulled out and at least one 12 x 12 hole to be able to replumb down to the dishwasher and kitchen sink. Outside hose bibs would require 12 x 12 holes on the interior side of the walls. Toilets I'm not sure...forget to ask him. Our Jacuzzi is incased in stone tiles with no apparent access, so he said we may just want to leave that alone otherwise it would require a lot of breaking to get to those lines.

As a layperson, I'm just trying to get some sense of what all is involved with the vertical repipe and if it's really true that PEX can be "fished" down at least some of the walls. He said that they can strap the lines up in the attic and down around the fixture and do on/off tests to see if the pipes rattle. If they do, then they would need to break a 12 x 12 somewhere midway down the wall to strap the line or something like that.

The PEX is a lot less damage. It also doesn't hammer around in the walls every time a faucet is turned off like unstrapped copper can.
The damage to the home will be much less with PEX.
During a repipe, you will want to replace the old tub faucets with the newer pressure balanced ones. And the Jacuzzi may just have to wait for the moment.

All good things to know. Thank you. I was initially leaning towards PEX, but then heard that one of the plumbers I got a quote from stopped installing PEX for liability reasons, but am now leaning towards it again b/c it seems that the plumbers in this forum don't have an issue with it, the fact that it's less destructive and that it may be easier/quicker to do for the plumber. If not PEX, my only other option is CPVC as we're in a hard water area. Want to stay away from copper.